For the first time, Apple support technicians have pointed at a manufacturing issue as the origin of the yellow bands and spots that people are finding in their iPhone 4's displays. There's no official word from Apple yet, however.
There's a problem with the iPhone 4's Retina displays: Some screens have a yellow tint across the surface. 55 cases and counting. In some, it's a yellow band. In others, yellow spots. See the gallery. [Updated with Apple support feedback]